1. Field of the Invention
This invention relates to molded case circuit breakers and more particularly to a gasket for a line conductor within a circuit breaker which assists in channeling conductive ionized gases resulting from a circuit interruption to designated vents in the circuit breaker housing to prevent such gases from flashing over and causing phase-to-phase and phase-to-ground faults.
2. Description of the Prior Art
Molded case circuit breakers are generally old and well known in the art. An example of such a circuit breaker is disclosed in U.S. Pat. No. 4,973,927. Such a circuit breaker is used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload and relatively high level short circuit condition. An overload condition is normally about 200-300 percent of the nominal current rating of the circuit breaker. A high level short circuit condition can be 1000 percent or more of the nominal current rating of the circuit breaker.
Molded case circuit breakers include at least one pair of separable contacts which may be operated either manually by way of a handle disposed on the outside of the case or automatically in response to an overcurrent condition. In the automatic mode of operation, the contacts may be opened by an operating mechanism, controlled by a trip unit, or blown open by magnetic repulsion forces generated between the stationary and movable contacts during relatively high levels of overcurrent.
Ionizing gases are generated within the circuit breaker as a result of a separation of the main contacts. Since such gases are conductive, communication of such gases between phases or between phase and ground can cause segregated and generally channeled through arc extinguishers and vented out the circuit breaker.
In order to segregate such ionizing gases, each pole of a multipole circuit breaker is segregated within the circuit breaker by way of interior sidewalls, known as interphase gas barriers, defining one or more phase compartments. An arc extinguisher is disposed in each phase compartment adjacent the separable main contacts. The arc extinguishers are typically formed with a plurality of parallel plates, carried by a frame which includes a rear wall and two sidewalls. The rear wall is provided with a plurality of vent holes which allow the ionizing gases generated in each phase compartment to be channeled through the arc extinguishers and discharged out dedicated vents, formed in the circuit breaker cover on the line side of the circuit breaker.
It is also important to minimize communication of the ionizing gases between adjacent the line side terminals, generally disposed outside the circuit breaker housing. More specifically, the line side conductors are received in openings in one wall of the housing such that the line side terminals extend outwardly therefrom. In order to prevent communication of the ionizing gases between adjacent line side terminals, exterior interphase gas barriers are provided. Removable line terminal covers are also provided which, in addition to allowing access to the line terminals, also act as interphase gas barriers adjacent the vents through which the ionizing gases are discharged in the circuit breaker cover.
Moreover, due to the difference in potential between the line conductor and the movable contact arm assembly after the main contacts open, it is also necessary to reduce the amount of ionizing gases that communicate therebetween, particularly where the separation between the line conductor and the movable contact arm assembly is the smallest to prevent flashover. Lastly, it is necessary to seal the interfaces within the phase compartments between the line conductor and the housing in order to prevent communication of the ionizing gases between phases and between phases and grounded components, such as the panelboard, which carries the circuit breaker. These interfaces include the openings in the wall of the housing through which the line conductor extends and the wall of the housing to which the line conductor is secured. It is known in the art to seal such interfaces as well as form a gas barrier between the line conductor and the movable contact arm with amorphous sealing compounds, such as SIKAFLEX-221, available from R.R.B. Plastics in Waldron, Ind. or RTV, available from the hand. Not only is such a process time-consuming which leads to increased labor costs, but it is difficult to obtain consistent results. Moreover, although proper application of the sealant can provide an effective gas seal and barrier, improper application by less experienced personnel can lead to an ineffective seal or barrier which can result in a circuit breaker failure.